.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.TH MPI_File_read_ordered_begin 3 "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
.SH NAME
\fBMPI_File_read_ordered_begin\fP \- Reads a file at a location specified by a shared file pointer; beginning part of a split collective routine (nonblocking).

.SH SYNTAX
.ft R
.nf
C Syntax
    #include <mpi.h>
    int MPI_File_read_ordered_begin(MPI_File \fIfh\fP, void \fI*buf\fP, 
    	      int \fIcount\fP, MPI_Datatype \fIdatatype\fP)

.fi
.SH Fortran Syntax
.nf
    INCLUDE 'mpif.h'
    MPI_FILE_READ_ORDERED_BEGIN(\fIFH\fP, \fIBUF\fP, \fICOUNT\fP, \fIDATATYPE\fP,\fI IERROR\fP)
		<type>		BUF(*)
        	INTEGER		FH, COUNT, DATATYPE, IERROR

.fi
.SH C++ Syntax
.nf
#include <mpi.h>
void MPI::File::Read_ordered_begin(void* \fIbuf\fP, int \fIcount\fP,
	const MPI::Datatype& \fIdatatype\fP)

.fi
.SH INPUT/OUTPUT PARAMETER
.ft R
.TP 1i
fh    
File handle (handle).

.SH INPUT PARAMETERS
.ft R
.TP 1i
count
Number of elements in buffer (integer).
.ft R
.TP 1i
datatype
Data type of each buffer element (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
buf
Initial address of buffer (choice).
.TP 1i
IERROR
Fortran only: Error status (integer). 

.SH DESCRIPTION
.ft R
MPI_File_read_ordered_begin is the beginning part of a split collective, nonblocking routine that must be
called by all processes in the communicator group associated with the
file handle 
.I fh.
Each process may pass different argument values for the 
.I datatype 
and 
.I count 
arguments. Each process attempts to read, from the file associated with 
.I fh,
a total number of 
.I count 
data items having 
.I datatype 
type into the user's buffer 
.I buf.
For each process, the location in the file at which data is read is the position at which the shared file pointer would be after all processes whose ranks within the group are less than that of this process had read their data. 

.SH NOTES
.ft R
All the nonblocking collective routines for data access are "split" into two routines, each with _begin or _end as a suffix. These split collective routines are subject to the semantic rules described in Section 9.4.5 of the MPI-2 standard. 

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI:Exception object.
.sp
Before the error value is returned, the current MPI error handler is
called. For MPI I/O function errors, the default error handler is set to MPI_ERRORS_RETURN. The error handler may be changed with MPI_File_set_errhandler; the predefined error handler MPI_ERRORS_ARE_FATAL may be used to make I/O errors fatal. Note that MPI does not guarantee that an MPI program can continue past an error.  

